Planographic printing plate and method of making the same



iatentecl Apr. 25, 1939 UNITED STATES PLANOGRAPHIC PRINTING PLATE AND METHOD OF MAKING THE SAME Francis L. Simons, Montclair, N. J.

No Drawing. Application August 24, 1936, Serial No. 97,598. Renewed September 26, 1938 13 Claims.

The present invention relates to planographic printing surfaces and more particularly to flexible composite planographic printing plates adapted for use in lithography, either offset or direct, and

to methods of making the same.

The planographic printing surfaces provided by my invention, while satisfactory for planographic and lithographic printing generally, are more particularly suitable for the reproduction of what is known to the art as direct images, such as wax crayon drawings, typewriting, etc. which may be placed directly upon the printing surface without the intervention of any photographic process. The printing surfaces of this invention 35 are also suitable for use Where photographic methods are employed, providing that the customary photo-sensitizing coatings are neutral or acid in reaction instead of alkaline as in common practice.

26 It is an object of this invention to provide an improved planographic printing surface which will be suitable for use with both photographic and hand transfer (direct) methods of application of the image. It is a further object of the 25 invention to provide a composite lithographic plate of suificient flexibility so that it may be used directly in the typewriter for application of direct' images.

Planographic printing, as is well known, comprises printing from a smooth surface containing areas which are covered with ink and areas which remain blank.

In the course of the printing operation the ink on the printing or image areas must be period- 95 ically renewed, usually after each successive copy is printed. However, it is impracticable to apply ink with any mechanical device to a planographic printing image without having the inking device also come in contact with the blank areas, and it 40 is therefore necessary in planographic printing to provide means whereby the original blank areas will remain blank and continuously refuse to take up any ink from the inking devices on the printing press. At the same time, any such means so provided must not interfere with the continuous application to and retention of ink by the printing or image areas.

Stone, zinc, and aluminum are the most com- 50 monly used materials for planographic printing and the division of the printing art which uses these three materials is commonly known as lithography or lithographic printing. The essential features of lithographic printing are first the 55 provision of a plane surface which is inherently attractive to printing ink and to greasy and oily marking materials in general; secondly, the provision in this surface of the additional property of becoming desensitized or repellent to printing ink and other greasy materials when such 6 surfaces are chemically treated by methods which have been developed in the art over a long period of years. In stone. these two properties are a natural function of the porosity, absorbency, and surface texture or grain of the stone itself. In 10 zinc and aluminum, the first of these properties,-attraction for ink-is an inherent quality of metals, while the second property is partly due to artificially graining the surface by light abrasion, and partly due to the chemical reacll tivity of the metals; The use of stone, zinc, and aluminum surfaces in lithography, therefore, includes the application of a greasy image to such a grained or matte surface either directly or by the use of photography, which step is followed by a treatment of the remainder of the surface with certain chemical reagents such as gum arabic, phosphoric acid, etc., so to change the character of the metal or stone that printing ink will no longer adhere to it if any traces of Water are present. Those skilled in the art refer to this chemical treatment as desensitizing or counter-etching. By the foregoing means, pianographic printing surfaces are provided which can be used for printing in special presses where the printing surface is alternately contacted with an inking device and with amoistening device. During the printing operations the printing plates so prepared continually take up ink on the image areas and transfer it to the print, while the i blank areas take up water from the moistening device and likewise transfer it to the print. As I printing inks and water are mutually immiscible, there is no encroachment of one upon those portions of the plate occupied by the other. 49

As a further precaution to aid in keeping the blank areas blank, the press operator may add to the water used in the printing press moistening device a small amount of the same or similar chemicals as were used in the counter-etch or desensitizing operation. Glycerine has also been used as a further adjuvant to maintain the blank areas of the plate thoroughly wettable by water and therefore ink-repellent.

As a matter of clearness, the moistening fluid used in the printing press will be hereafter referred to as the-repellent whether it comprises plain water, or water to which gum arabic, phosphoric acid, glycerine, ammonium salts, etc. have 5' been added. Similarly, the chemicals or solutions used in the original treatment of the'blank areas of the plate to render them water-retentive and ink-repellent will be referred to as desensitizers".

I have discovered that certain water-insoluble coatings as herein described may be converted into lithographic surfaces by treatment which involves partially dissolving or softening the coating and then drying the same.

In the preferred practice of my invention, I first provide a sheet of flexible material, which may for example be paper, paper board, fibre, or suitable textile fabric. The sheet is preferably sufliciently thin and flexible to bend around a typewriter platen, but it should have the necessary strength for use on offset or rotary presses.

This flexible sheet is preferably waterproofed, for example by varnishing or by impregnation with any convenient wax or resin composition. I may also use two or more plies of thin material such as paper stuck together with asphalt or other suitable waterproof adhesive.

The degree of waterproofing may vary with the proposed use for the finished plate. For short runs of low quality printing it is not essential to achieve perfect waterproofing, while for longer runs of high quality work the base should be sufliciently waterproof to prevent misregister due to expansion.

To one or both surfaces of this flexible sheet, I apply a coating material which comprises a filler and a water-soluble binder, and which dries to a hard, compact, water-insoluble film or coating on the sheet. While this coating should be flrm, hard and coherent, it should also be sufficiently flexible to bend with the paper base and must not be brittle or subject to flaking or scaling. In addition, the coating must adhere firmly to the sheet, even when moistened with water or other repellent used on offset presses.

Various compositions and mixtures are suitable for this coating. As examples of suitable binders, casein, glue, shellac, rosin and albumin may be mentioned. As examples of suitable fillers, mention may be made of clay, calcium sulphate, titanox, lithopone, silica and the like. In addition, formaldehyde may advantageously be included as an insolubilizing agent, and small amounts of water-miscible organic solvents such as methyl cellosolve may be added to promote firm anchorage to the base sheet.

While the use of fillers or pigments in the coating is not absolutely essential, I find it preferable to incorporate them, since they promote flexibility and also afford means of obtaining a high white color in the finished product.

Essentially, my coating thus comprises a firm, compact, adherent film which is substantially water-insoluble after it is once dried, but which may be partially redissolved or softened by alkalies, and which will return to its water-insoluble condition again after redrying.

Water 65 Example 2 Per cent Rosin 4 Ammonia 4 Titanox 10 Water 82 Depending on the hardness and purity of the grade of rosin used, one-half to five percent of rosin oil or similar softener may be added to promote flexibility.

Example 3 Per cent Glue- Alum Glycerine 2 Hexa methyline tetramine 1 Silica 30 Water 60 ordinary commercial sodium silicate and dilute it with five to fifteen volumes of water. The resulting solution is applied to the coating as by brushing, flowing or in any other convenient manner, and is allowed to stand in contact with the coating for a short time, sufficient to permit the casein, glue or other binder in the coating to become soft and plastic, due to the solvent action of the alkaline silicate.

In this plastic condition, the coating is subjected to continuous, rapid agitation, as by brushing or scrubbing, and the agitation is continued during the brief period required for the softened and moist coating to dry out and harden sufficiently to retain the roughened surface or "gra.in imparted by this treatment. After a short period of further drying, either at room temperature or higher, the plate is ready for use.

Instead of sodium silicate mentioned in the foregoing example, I may use any convenient alkali or alkaline salt, such as borax, lime, trisodiumphosphate, sodium aluminate and the like. I prefer in general to use alkaline salts which furnish an insoluble residue from their own structure. For example, sodium silicate, after interaction with the base coating of my composite plate, will produce precipitated silica. Similarly, sodium aluminate furnishes a considerable volume of precipitated alumina or aluminum hydroxide. The additional solid matter derived from these alkalies becomes mixed and blended with the softened casein or other coating material during the final period of agitation. This has, among other beneficial results, the effect of adding to the total amount of filler used in the film.

The agitation described above imparts a porous texture of grain to the surface of the coating, which renders this surface properly receptive to ink and other lithographic marking materials. The surface of my plate is also properly reactive to lithographic desensitizers.

I claim:

1. A planographic printing plate adapted for use in lithographing, comprising a backing sheet composed of a material which is substantially non-stretching when subjected to the lithographing process, said sheet having thereon a flexible, substantially water-insoluble coating including an insoluble residue resulting from the reaction of a basic salt with other ingredients of the coating.

2. A planographic printing plate adapted for use in lithographing, comprising a backing sheet composed of a material which is substantially non-stretching when subjected to the lithographing process, said sheet having thereon a substantially water-insoluble coating including precipitated silica.

3. In a process for preparing a lithographic plate, the steps which comprise providing a plastic surface on said plate, imparting a lithographic grain to said surface by agitating the same while in a plastic condition, then solidifying the surface to maintain the lithographic grain thereon.

4. A process for preparing a plate for use in lithography which comprises preparing a backing sheet by treating a sheet of paper to render the same substantially waterproof and non-stretching when subjected to the lithographic process, applying to said backing sheet a coating of a material which will adhere tenaciously to said sheet and provide a substantially water-insoluble coating thereon, said coating being capable of being rendered plastic, and roughening the surface of said coating while in a plastic condition.

5. A process for preparing a lithographic plate which comprises applying over a backing sheet a coating of a material which will adhere tenaciously to said sheet and provide a substantially water-insoluble coating thereon, said coating being capable of being rendered plastic, drying said coating, then rendering the surface of said coating plastic and agitating the same while in a plastic condition.

6. A process of preparing a lithographic plate which comprises providing a flexible backing sheet which is substantially non-stretching when subjected to the lithographing process, coating said sheet with a coating comprising a filler and a water-soluble binder, said coating being capable of being rendered plastic, drying said coating to produce a flexible, substantially water-insoluble coating on the sheet, then rendering the surface of said coating plastic and agitating the same while in a plastic condition, and then drying the coating.

'7. A process of preparing a lithographic plate which comprises providing a flexible backing sheet which is substantially non-stretching when subjected to the lithographing process, coating said sheet with a coating comprising a filler, casein and formaldehyde, imparting lithographic properties to the surface of said coating by roughening the same while in a plastic condition. and drying the coating.

8. In a process of preparing a plate for use in lithography, the steps which comprise providing a flexible backing sheet which is substantially non-stretching when subjected to the lithographing process, coating said sheet with a coating material which forms on said sheet a substantially water-insoluble coating capable of being rendered plastic by alkalis or alkaline salts, rendering the surface of said coating plastic by applying thereto an alkaline liquid, agitating the surface of said coating while in a plastic condition, and drying, the coating.

.9. In a process of preparing a plate for use in lithography, the steps which comprise providing a flexible backing sheet, coating said sheet with a coating material which forms on said sheet a substantially water-insoluble coating capable of being rendered plastic by alkalis or alkaline salts, rendering the surface of said coating plastic by applying thereto a solution of an alkaline salt, agitating the surface of said coating while in a plastic condition to impart lithographic properties thereto, and drying the coating.

10. In a process of preparing a plate for use in lithography, the steps which comprise providing a flexible backing sheet, coating said sheet with a coating material which forms on said sheet a substantially water-insoluble coating capable of being rendered plastic by alkalis or alkaline salts, rendering the surface of said coating plastic by applying thereto a solution of an alkaline salt which, upon reaction with other ingredients of the coating, deposits an insoluble residue, agitating the surface of said coating while in a plastic condition, and drying the coating.

11. In a process of preparing a plate for use in lithography, the steps which comprise providing a flexible backing sheet which is substantially non-stretching when subjected to the lithographic process, coating said sheet with a coating material which forms on said sheet a substan tially water-insoluble coating capable of being rendered plastic by sodium silicate, rendering the surface of said coating plastic by applying thereto sodium silicate, agitating the surface of said coating while in a plastic condition and drying the coating.

12. A process of preparing a plate for use in lithography comprising coating 9. sheet of water repellent paper with a coating comprising silicious clay and a binder, drying the plate, treating the surface of the plate at least partially to redissolve the binder, then drying the plate.

13. A process of preparing a lithographic plate comprising coating a sheet of waterproof paper with a coating comprising silicious material and a casein binder, drying the plate, rendering the surface of the plate alkaline to soften the binder and again drying the plate, whereby is produced a flexible lithographic plate having a surface texture which exhibits a definite affinity both for water and for lithographic marking material.

FRANCIS L. BIMONS. 

